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s Ci¢ologecal7¢cknccslxc Page 6 Groundwater Monitoring Report Project No 770 2 September 24, 2003 ' + Minor BTEX constituents are resent at levels ranging from 0 3 — I 1 /1 in wells MW- 4, MW-5, MW-6 and MW-7 • Motor oil range petroleum hydrocarbons were not present in any of the groundwater samples at concentrations above the laboratory reporting limits • Deep wells MW-104, MW-105 and MW-106 did not contain contaminant concentrations above the laboratory reporting limits for the second consecutive event • The lateral extent of the diesel groundwater plume is currently undefined to the south ' • The vertical extent of the plume is intermittently defined by MW-104, 105, & I06 + Oxidation-Reduction Potential (ORP) measurements show that one monitoring well is within the reaction depleted water caused by biodegradation of the contamination ' plume Well MW-7 exhibited a negative ORP value and all of the wells' ORP data are included in Table 5 of Appendix A The other wells have varying positive values suggesting that the water around these wells is outside of or on the outer fringe of the impacted halo ' An examination of the contaminant distribution and groundwater flow direction data doesn't reveal any obvious trends A consistent factor previously noted in the investigation was the increase in diesel concentrations in well MW-5, see Figure 6- MW-5 TPH-D vs Groundwater Elevation The concentrations had previously demonstrated an increasing trend until June 2002 when wide fluctuations began The well has displayed decreasing concentrations for the past two events The plot in Figure 5 suggests a predominant direct relationship between groundwater elevation and contaminant concentrations Well MW-4 lies adjacent to the former UST field Figure 7- MW-4 TPH-D vs ' Groundwater Elevation suggests an inverse relationship between groundwater elevation and contaminant concentrations in well MW-4 Well MW-5 continues to contain the highest concentrations of detected contaminants (see Figure S) It has not been down gradient of the former UST location for the monitoring events completed by GTI to date The reason for this anomaly is not known, but could be related to geologic units that slope to the west Since none of the deep wells contained TPH-D, a contour diagram was not produced In Figure 9--- MW-5 & MW-105 TPH-D versus Groundwater Elevation, well MW-5 contaminant concentrations have generally correlated with changes in the water table Well ' MW-105, screened below the water table, exhibits a typically inverse relationship between contaminant concentrations and groundwater elevation